The invention has its origin in problems associated with slender cutting tools of the type that include two parts interconnected via an interface or a coupling, the parts being a long narrow basic body and a cutting body or wear part that is detachably connected with the same and of the type that is denominated loose top by those skilled in the art. In practice, such tools may be rotatable and be in the form of drills or milling cutters, e.g., shank-end mills or contour mills. In these tools, the basic body is usually manufactured from steel and the loose top from cemented carbide or the like, i.e., a material that is harder than steel by having a considerably greater modulus of elasticity than steel. The most common type of coupling between the basic body and the loose top makes use of a male member that protrudes from the rear end of the loose top and is inserted into and locked in a seating in the front end of the basic body. Many tools of the kind in question are fairly slender so far that their length is many times greater than the diameter. It is then—with the purpose of counteracting bending phenomena and vibrations—desirable to improve the stiffness and stability of the basic body by manufacturing the same from a material that has a greater modulus of elasticity than steel, e.g., cemented carbide. However, if the male and female coupling between the basic body and the loose top require grinding or another precision machining, such as is the case with thread couplings, problems arise, because internal machining in cemented carbide is difficult, if not impossible, to carry out with good precision.
In order to solve the above-mentioned problems, it has previously been tried to solder a steel body onto the front end of a part body of cemented carbide or the like, in the front end of which steel body a female thread can be ground internally. However, this solution has turned out to be unreliable because soldering is a manual operation, which lacks accurate repeatability. In other words, the important coaxiality between the steel body and the cemented carbide body may be difficult to attain. In addition, the soldered seam forms in practice a permanent joint, which entails that the basic body in its entirety has to be discarded also in such cases when only the front steel body is damaged, but not the rear cemented carbide body.
Another proposed solution is presented in U.S. Pat. No. 6,312,201 B1, which shows a cutting tool of the initially generally mentioned kind. More precisely, the cutting tool in question includes front and rear tool bodies of cemented carbide or the like, which are formed with male members each surrounded by a ring of steel, which is, shrunk onto the male members. However, the shrink fit has the disadvantage that replacement of worn loose tops become highly intricate and time-consuming. In addition, the coaxiality of the loose top and basic body may be impaired if the generation of heat in the tool becomes great.
The present invention aims at obviating the above-mentioned disadvantages of previously known tools of the kind in question and at providing an improved tool. Therefore, an object of the invention is to provide a tool, the basic body of which can be generally made of cemented carbide or another stiff material, and in spite of this be formed with a seating that can be machined internally at high accuracy. In particular, it should be possible to form the seating of the basic body with a precision-machined female thread for the co-operation with an externally ground male thread of a male element included in the loose top, with the purpose of attaining a good coaxiality and a reliable interconnection of the loose top and the basic body.
Another object of the invention is to provide a tool, the coupling of which between the loose top and the stiff basic body allows quick mounting and dismounting of the loose top.
Yet another object of the invention is to provide a tool, the basic body of which to a major extent can be re-used, even if the front part thereof adjacent to the seating would be damaged or in another way become unusable.